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Intensive agricultural production with insufficient organic fertilization, as expected, results in a decrease of organic matter content in the soil. Analyses of soil fertility in the Republic of Croatia over two years (2019 and 2020) showed that there is less than 2% SOM in 52.1% of analyzed soils (10, 283 samples), with the average humus content in these soils being only 1.61%. Also, less than 3% humus was found in as many as 87.9% of soil samples (17, 339 samples) with an average humus content of 1.92%. At the same time, as part of the research on the impact of land use on changes in soil properties after a 15-year period, a decrease in the content of organic matter in the soil was determined on arable land. The consequence of low humus content, along with insufficient mineralization potential, is a decreasing of soil elasticity, i.e. the inability of the soil to adapt to the negative impacts of climate change, primarily the increasing amplitudes of soil temperature and humidity. The increasing importance of organic fertilization and manure is also emphasized by the multiple increase in the price of mineral fertilizers, 2.2 to 4.1 times (2022 compared to 2018). Therefore, it is necessary to optimize organic fertilization, both because of the need for fertilization and for the environment protection. With the aim of optimizing fertilization in Croatia, in 2021, 610 manure samples were analyzed for 22, 121 ha of arable land planned to be fertilized (4, 266 soil samples analyzed, average 2.26% humus, 42.9% soil with 100 kg/ha P2O5 or K2O) in phosphorus fertilization at 56% and potassium at 34.1% of the soil, but about 1/5 of these soils are already rich in phosphorus (20.6 %) or potassium (17.5 %) and a positive balance is not required. Organo-mineral fertilization will result in a negative five-year balance of phosphorus at 20.4% and potassium at 38.4% of the soils, but 88.1% of these soils are already rich in phosphorus and 48.0% rich in potassium and the balance could be negative. The cumulative effect of organo-mineral fertilization over 5 years will result in a lower need for mineral forms of N, P and K and mineral fertilization could be reduced to an average of 26% of the amount of urea compared to mineral fertilization without the use of manure, on 40% of the amount of N in the topdressing (e.g. CAN), on 35% of phosphorus fertilizers, and on 23% of potassium fertilizers. |
